Biopsy and sampling needle antennas for magnetic resonance imaging-guided biopsies

ABSTRACT

Herein is disclosed a magnetic resonance imaging antenna, including an inner conductor, an outer shield slideably displaceable with respect to the inner conductor, and an insulator electrically insulating the inner conductor from the outer shield. Herein is disclosed a biopsy needle antenna, including a magnetic resonance imaging antenna, having an outer shield, and an inner conductor electrically insulated from the outer shield by a dielectric; and a biopsy needle electrically connected to the inner conductor and electrically insulated from the outer shield by the dielectric. Herein is disclosed a method of obtaining a sample with magnetic resonance imaging guidance, including providing a sampling needle magnetic resonance imaging antenna, advancing the antenna to a structure from which the sample is to be taken, detecting magnetic resonance data by the antenna, and coupling the sample to the antenna.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/360,144, filed Jul. 26, 1999, now abandoned, which is acontinuation-in-part of U.S. patent application Ser. No. 08/638,934,filed Apr. 25, 1996, now U.S. Pat. No. 5,928,145. This application alsoclaims benefit of priority to U.S. Provisional Patent Application Ser.No. 60/286,271, filed Apr. 5, 2001, entitled “Biopsy Needle Antenna forMR Guided Biopsies.” The aforementioned applications are incorporatedherein in their entireties by this reference.

FIELD

The disclosed systems and methods relate to magnetic resonance imagingantennas, and in some embodiments to magnetic resonance imaging antennasadapted for use as biopsy or sample needles.

BACKGROUND

The advantageous use of magnetic resonance technology in providing safe,rapid images of a patient has long been known. It has also been known toemploy magnetic resonance technology in producing chemical shift spectrato provide information regarding the chemical content of a material.

In a general sense, magnetic resonance imaging involves providing burstsof radio frequency energy on a specimen positioned within a mainmagnetic field in order to induce responsive emission of magneticradiation from the hydrogen nuclei or other nuclei. The emitted signalmay be detected in such a manner as to provide information as to theintensity of the response and the spatial origin of the nuclei emittingthe responsive magnetic resonance signal. In general, imaging may beperformed in a slice or plane, in multiple planes, or in athree-dimensional volume with information corresponding to theresponsively emitted magnetic radiation being received by a computerwhich stores the information in the form of numbers corresponding to theintensity of the signal. The pixel value may be established in thecomputer by employing Fourier Transformation which converts the signalamplitude as a function of time to signal amplitude as a function offrequency. The signals may be stored in the computer and may bedelivered with or without enhancement to a video screen display, such asa cathode-ray tube, for example, wherein the image created by thecomputer output will be presented through black and white presentationsvarying in intensity, or through color presentations varying in hue andintensity. See, generally, U.S. Pat. No. 4,766,381.

One of the beneficial end uses of the disclosed systems and methods isin connection with atherosclerotic disease which is a major cause ofmortality and morbidity in the United States. Localized forms of thedisease, such as the deposit of plaque on the walls of blood vessels,can restrict local blood flow and require surgical intervention in someinstances. While angiography is an effective means for detecting theluminal narrowing caused by plaque, it does not provide informationregarding the nature of the process leading to blood flow reduction.Unfortunately, therapeutic methods, such as intravascular intervention,may experience failure due to the lack of sufficiently precise imagingmethods. An imaging system capable of providing detailed, qualitativeand quantitative data regarding the status of vascular walls at the timeof surgical intervention, could favorably influence the outcome byenabling the selection of the intervention method to be customized tothe particular need. It would also serve to provide precise guidance forvarious forms of localized therapy.

It has been known to use angioplasty and intravascular ultrasound forimaging plaques. See, generally, Spears et al., “In Vivo CoronaryAngioscopy,” Journal of the American College of Cardiology, Vol. 1, pp.1311–14 (1983); and Waller et al., “Intravascular Ultrasound: AHistological Study of Vessel During Life,” Circulation, Vol. 85, pp.2305–10 (1992). Intravascular ultrasound, however, provides severaldrawbacks, including the insensitivity to soft tissue and the inabilityto reliably detect thrombus and discriminate thrombus (new or organized)superimposed upon plaque from soft lipid-laden plaques. Also, thepresence of artifacts related to transducer angle relative to the vesselwall, and an imaging plane limited to the aperture of the transducer invariable resolution at different depths of view are further problemswith this approach.

The feasibility of identification of atherosclerotic lesions byemploying magnetic resonance (MR) microimaging in vitro has previouslybeen suggested. See, for example, Pearlman et al., “Nuclear MagneticResonance Microscopy of Atheroma in Human Coronary Arteries,” Angiology,Vol. 42, pp. 726–33 (1991); Asdente et al., “Evaluation ofAtherosclerotic Lesions Using NMR Microimaging,” Atherosclerosis, Vol.80, pp. 243–53 (1990); and Merickel et al., “Identification and 3-dQuantification of Atherosclerosis Using Magnetic Resonance Imaging,”Comput. Biol. Med., Vol. 18, pp. 89–102 (1988).

It has also been suggested that MRI can be used for quantification ofatherosclerosis. See, generally, Merickel et al., “NoninvasiveQuantitative Evaluation of Atherosclerosis Using MRI and ImageAnalysis,” Arteriosclerosis and Thrombosis, Vol. 13, pp. 1180–86 (1993).

Yuan et al., “Techniques for High-Resolution MR Imaging ofAtherosclerotic Plaques,” J. Magnetic Resonance Imaging, Vol. 4, pp.43–49 (1994) discloses a fast spin echo MR imaging technique to imageatherosclerotic plaques on an isolated vessel that has been removed bycarotid endarterectomy. As the signal-to-noise ratio (SNR) decreaseswith the decrease in imaging time and increase in resolution, specialradio frequency (RF) receiver coils were designed. The article suggeststhat by the use of special MR hardware at 1.5 T using various T1 andT2-weighted pulse sequences, it is possible to discriminate foam cells,fibrous plaque organized thrombus, new thrombus, loose necrosis andcalcium.

It has also been suggested that the fat content of atheroscleroticplaque in excised tissue samples can be determined using chemical shiftimaging or chemical shift spectroscopy. See, generally, Vinitski et al.,“Magnetic Resonance Chemical Shift Imaging and Spectroscopy ofAtherosclerotic Plaque,” Investigative Radiology, Vol. 26, pp. 703–14(1991); Maynor et al., “Chemical Shift Imaging of Atherosclerosis at 7.0Tesla,” Investigative Radiology, Vol. 24, pp. 52–60 (1989); andMohiaddin et al., “Chemical Shift Magnetic Resonance Imaging of HumanAtheroma,” Br. Heart J., Vol. 62, pp. 81–89 (1989).

The foregoing prior art articles in the aggregate could lead one skilledin the art to conclude that MR, while having potential for fullycharacterizing vessel wall disease, suffers from low anatomic resolutionunless used in vitro on small specimens with high resolution methods.

It is known that in order to obtain the desired high-resolution imagingand spectroscopy of arteriosclerotic plaques, a coil can be placed closeto the target blood vessel.

In Kantor et al., “In vivo ³¹P Nuclear Magnetic Resonance Measurementsin Canine Heart Using a Catheter-Coil,” Circulation Research, Vol. 55,pp. 261–66 (August 1984), there is disclosed an effort to improve theSNR in the ³¹P spectroscopy of a dog myocardium using an ellipticalcoil. This coil is rigid, rather bulky, and designed for spectroscopy ofthe myocardium, but is not ideal for vessels.

Disclosures of efforts to develop catheter coils for imaging vesselwalls are contained in Martin et al., “MR Imaging of Blood Vessel withan Intravascular Coil,” J. Magn. Reson. Imaging, Vol. 2, pp. 421–29(1992); and Hurst et al., “Intravascular (Catheter) NMR Receiver Probe:Preliminary Design Analysis and Application to Canine IliofemoralImaging,” Magn. Reson. Med., Vol. 24, pp. 343–57 (April 1992). Thesedisclosures employ two tiny diameter, back-to-back solenoid coils toproduce a good axial profile when the coils are placed along the mainmagnetic field.

Martin et al., “Intravascular MR Imaging in a Porcine Animal Model,”Magn. Reson. Med., Vol. 32, pp. 224–29 (August 1994) discloses use ofthe system disclosed in the above-cited Martin et al. article forhigh-resolution images of live animals. See, also, Abstract, McDonald etal., “Performance Comparison of Several Coil Geometries for Use inCatheters,” RSNA 79th Scientific Meeting, Radiology, Vol. 189(P), p. 319(November 1993). A strong disadvantage of these disclosures is thatmultislice acquisition cannot be carried out because the longitudinalcoverage of the sensitive regions is limited to a few millimeters.Furthermore, the coil itself does not have the desired flexibility whilemaintaining the desired efficiency of data acquisition.

U.S. Pat. No. 5,170,789 discloses a nuclear magnetic resonance (NMR)coil probe, in the form of a loop, that is said to be insertable withina specimen, which has an opening, for purposes of nuclear magneticresonance spectroscopy (NMRS). The disclosed two component probe, whichis in the nature of an endoscope to examine the colon or cervix, has afirst portion which is insertable into a body cavity and a secondportion which is external to such cavity. The probe has a flexible coilbody with an oval or circular shape that may deform during insertion. Asa result, the coil may require tuning after insertion. If the coil weremade of a very rigid material, insertion problems may occur. Also, atuning and matching circuit, in the external portion, may limit thedepth of insertion.

U.S. Pat. No. 4,932,411 discloses a probe with a transmit/receive coilfor insertion in channels which are surgically or otherwise inserted inbody organs, such as the brain, liver or kidneys. The coil, which is inthe form of a loop, is carried and wound on the distal end of a carrierwhich is used to insert the coil into the body channel.

U.S. Pat. No. 4,672,972 discloses an NMR probe disposed at the distalend of a catheter or endoscope for obtaining NMR spectra from within apatient. The multi-turn probe has a parametric amplifier and/or agate-array attached to it and, also, has a coil cooling system.

U.S. Pat. No. 5,413,104 discloses an invasive MRI transducer having aballoon, at least one lumen, and a flexible coil loop for insertion in abody cavity.

It has been known to employ an MR-active invasive device with RFtransmitter coils for selective MR angiography of blood vessels. See,generally, U.S. Pat. No. 5,447,156.

It has also been known to employ an intravascular catheter with aFaraday screen to prevent RF electric-field interactions with thesample, such as blood, which cause the coil to detune. See, generally,U.S. Pat. No. 5,419,325.

MR compatibility characteristics of various catheter and guide wiresystems, for use in interventional MR procedures, has been considered.See Dumoulin et al., “Real-time Position Monitoring of Invasive DevicesUsing Magnetic Resonance,” Magnetic Resonance in Medicine, Vol. 29, pp.411–15 (March 1993); and Abstract, Koechli et al., “Catheters and GuideWires for Use in an Echo-planar MR Fluoroscopy System,” RSNA 79thScientific Meeting, Radiology, Vol. 189(P), p. 319 (November 1993).

McKinnon et al., “Towards Visible Guidewire Antennas for InterventionalMRI,” Proc. Soc. Mag. Res., Vol. 1, p. 429 (August 1994) disclosesantenna designs which are asserted to make guidewires, biopsy or sampleneedles and other vascular interventional devices visible by MRI. OneMRI stub antenna is a length of coaxial cable with 10 cm of the braidremoved from the end. One end of the coaxial cable is directly connectedto the surface coil input of an MRI scanner and the other end is placedin a water filled phantom. The MR image is a bright line correspondingto spins in the immediate neighborhood of the cable. A preferred MRIstub antenna is an unterminated twisted pair cable having a diameter of0.2 or 1 mm, and a corresponding image line width of 1 or 3 mm,respectively, which provides a finer image than the coaxial cable stubantenna. A preferred combination is a steerable guidewire containing atwisted pair cable. It is suggested that a surface coil could be usedsimultaneously with a guidewire antenna by combining, as with phasedarray coils, the specimen image from the surface coil with the image ofthe stub antenna using the data acquired from the stub antenna, tolocalize the in vivo device during interventional MRI.

It has been known to employ an invasive device having an RF coil fortransmitting RF signals which are detected by external RF receive coilsto track the invasive device. See, generally, U.S. Pat. No. 5,437,277.

It has also been known to employ external RF transmitter/receiver coils.See, generally, U.S. Pat. No. 5,447,156.

U.S. Pat. No. 5,323,778 discloses a probe for insertion in an artery orother body passageway. The probe has an MRI coil, an external MRI RFsource and an RF heating apparatus for hyperthermia therapy.

Japanese Kokai Patent Application No. Hei 6[1994]-70902 to Koshiichi(hereinafter “Koshiichi”) discloses two forms of dipole antenna. Thefirst form has four wires and three ends. Two input leads are providedand two conducting poles form the dipole. One pole is inserted into abody cavity while the other is outside the body. The length of theinserted pole is about 1.2 meters at the field strength of 1.5 T commonto many whole-body MRI systems today, resulting in a total antennadipole length of about 2.4 meters. This three-ended dipole isimpractical and/or has major practical disadvantages because i) the polelength is too long for applications to body cavities, blood vessels,etc.; ii) the inserted pole is loaded by the body impedance to an extentwhich varies with the length inserted, resulting in the MRI resonantfrequency and match impedance varying with the length of insertion; iii)the fact that one end is inserted and the other end is not results inimbalancing of the impedance of the dipole which could deleteriouslyaffect safety and performance; iv) because the length of the poles iscomparable to the input leads, the tuning of the MRI resonant frequencyand the impedance matching of the coil will depend on the location,orientation, and bending of each pole relative to the other; v) becausethe pole length is so long (about 1.2 meters at 1.5 T) this MRI probewill perform poorly compared to preexisting MRI coils whose dimensionsare smaller, rendering it a disadvantageous probe design relative topre-existing MRI probe technologies, including ones designed for useexternal to the body (such as solenoid “bird cage” MRI coils, surfacecoils, etc.); and vi) it is impractical to maintain an orientation ofthe dipole relative to the magnetic field when such coil is introducedinto the convoluted and contorted passages of the body. For thesereasons, the first dipole antenna design of Koshiichi has significantimpediments for human applications.

Koshiichi further describes a second embodiment of his probe wherein oneof the poles is folded back and incorporated into a sleeve. While thismay partially overcome the problem of having a free end, the otherproblems discussed above with respect to his first embodiment remain. Inparticular, the 2.4 meter length is excessively long, has inferiorperformance with respect to existing MRI probes which do not allowinsertion, and the end with the single pole will interact with thesleeved end containing the other pole and the input leads, making itimpractical to tune.

U.S. Pat. No. 5,358,515 discloses a microwave hyperthermia applicatorfor limited heating of cancerous tissue including upper and lower dipolehalves of the same diameter. The upper dipole half is a widened metalextension of the inner conductor of an insulated coaxial cable. Thelower dipole half is a metal cylinder connected to the outer sheath ofthe coaxial cable. A π/2(λ/4) transformer, such as the outermost metalcylindrical sheath of a triaxial cable, is separated at its upper endfrom the lower dipole half which is connected to the coaxial cable outersheath. The transformer is filled with a dielectric medium and isconnected at its lower end to such coaxial cable outer sheath. When theantenna is inserted in a dissipative medium and supplied with microwaveenergy through the coaxial cable, only that area of the mediumimmediately around the antenna is heated.

MRI has many desirable properties for the diagnosis and therapy ofatherosclerotic disease. For example, it is possible to see lesionsdirectly, even before the plaques calcify. However, the SNR of MR imagesobtained from conventional surface or body coils is insufficient. Thisis because the coils placed outside the body pick up noise from a verylarge region of the body. To achieve satisfactory quality, the signalreceiver can be placed as close as possible to the tissue of interest(e.g., blood vessels). A coil placed on the tip of a catheter andinserted into the blood vessels could be a solution; but, the real partof the impedance of a catheter coil is relatively small and, hence, atuning and matching circuit is preferably located immediately after thecoil within the blood vessels. It is believed that prior art designsthat do otherwise suffer from a significant SNR loss. On the other hand,it is believed that prior art designs, which have a tuning and matchingcircuit immediately after the coil in blood vessels, are too thick to beplaced into small vessels.

There remains, therefore, a very real and substantial need for animproved apparatus and method for MR imaging and spectroscopic analysisof specimens in a manner which provides efficient data acquisition withmaximum SNR while permitting in vivo or in vitro acquisition from smallvessels and a wide range of other types of specimens.

SUMMARY

As used herein, the term “specimen” shall refer to any object other thana loopless antenna placed in the main magnetic field for imaging orspectroscopic analysis and shall expressly include, but not be limitedto members of the animal kingdom, including humans; test specimens, suchas biological tissue, for example, removed from such members of theanimal kingdom; and inanimate objects or phantoms which may be imaged bymagnetic resonance techniques, or which contain water or sources ofother sensitive nuclei.

As used herein, the term “loopless antenna” shall expressly include, butnot be limited to a dipole antenna and any and all equivalents thereof,such as, for example, a dipole antenna having two poles at least one ofwhich includes a mechanical loop (see, e.g., FIG. 14).

As used herein, the term “patient” shall mean human beings and othermembers of the animal kingdom.

As used herein, the term “composite image” shall mean a magneticresonance image that is formed from magnetic resonance data obtained bya magnetic resonance antenna and a magnetic resonance scanner, bodycoil, or surface coil. The data from the magnetic resonance antenna andthe magnetic resonance scanner, body coil, or surface coil may beobtained simultaneously or substantially simultaneously. An image formedby a biopsy or sampling needle antenna can preferably be a highresolution image, such as one millimeter resolution, submillimeterresolution, 300 micron resolution, 100 micron resolution, or 10 micronresolution.

In an embodiment, a biopsy or sample needle antenna includes a magneticresonance imaging antenna, having an outer shield, and an innerconductor electrically insulated from the outer shield by a dielectric;and a biopsy or sample needle electrically connected to the innerconductor and electrically insulated from the outer shield by thedielectric.

In an embodiment, a biopsy needle antenna may include a cannula beingformed at least in part of a conductive material, an obturator beingformed at least in part of a conductive material, the obturator beingslideably displaceable relative to the cannula, an insulatorelectrically insulating the cannula from the obturator, and a connectorthat can couple the cannula and the obturator to a magnetic resonanceinterface circuit.

In an embodiment, a sampling needle antenna may include a cannula beingformed at least in part of a conductive material, an obturator beingformed at least in part of a conductive material, the obturator beingslideably displaceable relative to the cannula, and an insulatorelectrically insulating the cannula from the obturator, wherein theouter shield, the inner conductor, and the insulator form a magneticresonance imaging antenna.

In an embodiment, a method of obtaining a sample with magnetic resonanceimaging guidance can include providing a sampling needle magneticresonance imaging antenna, advancing the antenna to a structure fromwhich the sample is to be taken, detecting magnetic resonance data bythe antenna, and coupling the sample to the antenna. In an embodiment, asample can be a biopsy.

In an embodiment, a biopsy or sample needle antenna can include acannula being formed at least in part of a conductive material, anobturator being formed at least in part of a conductive material, theobturator being slideably displaceable within the cannula, and aninsulator electrically insulating the cannula from the obturator,wherein the outer shield, the inner conductor, and the insulator form amagnetic resonance imaging antenna.

In an embodiment, a magnetic resonance imaging antenna can include aninner conductor, an outer shield slideably displaceable with respect tothe inner conductor, and an insulator electrically insulating the innerconductor from the outer shield.

In an embodiment, a method of obtaining a magnetic resonanceimaging-guided biopsy can include providing a biopsy or sample needlemagnetic resonance imaging antenna, advancing the antenna to a structurefrom which the biopsy is to be taken, detecting magnetic resonance databy the antenna, coupling the biopsy to the antenna.

In an embodiment, a method of obtaining a magnetic resonanceimaging-guided biopsy can include providing a biopsy or sample needleantenna, having a magnetic resonance imaging antenna, including an outershield, and an inner conductor electrically insulated from the outershield by a dielectric, and a biopsy or sample needle electricallyconnected to the inner conductor and electrically insulated from theouter shield by the dielectric; advancing the needle to a lesion,imaging the lesion with the antenna, and taking a sample of the lesionwith the needle.

An embodiment may further comprise a sheath, the biopsy or sample needlebeing slideably displaceable within the sheath. In an embodiment, thesheath can be defined by the outer shield.

In an embodiment, at least one of the outer shield, the inner conductor,and the biopsy or sample needle can include at least one of a magneticresonance compatible material, gold, sliver, copper, aluminum,gold-silver, gold-copper, silver-copper, platinum, and platinum-copper.

In an embodiment, the outer shield and the inner conductor can form acoaxial cable. In an embodiment, the coaxial cable may be electricallyinterconnected to an impedance matching circuit.

In an embodiment, at least one of the outer shield, the inner conductor,and the biopsy or sample needle can include at least one of asuperelastic material, platinum, iridium, MP35N, tantalum, Nitinol,L605, gold-platinum-iridium, gold-copper-iridium, titanium, andgold-platinum.

In an embodiment, the outer shield can be slideably displaceable withrespect to the inner conductor. In an embodiment, the inner conductorcan include an obturator and the outer shield comprises a cannulaslideably displaceable over the obturator. In an embodiment, theobturator can further include a side-slit. In an embodiment, the cannulacan include a distal end having a cutting edge, the cutting edgeslideably displaceable over the side-slit. In an embodiment, the cannulacan cover at least the side-slit.

In an embodiment, the cannula can be spring-loaded. In an embodiment, atleast a portion of the obturator can protrude from a distal end of thecannula. An embodiment can further include a spring coupled to the outershield. In an embodiment, the spring can be electrically coupled to theouter shield.

In an embodiment, the dielectric can include at least one offluroethylene polymer, tetrafluoroethylene, polyester, polyethylene,silicone, metal oxide, glass, and polyethylene terephthalate. In anembodiment, the dielectric can be covered by a lubricious coating. In anembodiment, the lubricious coating can include at least one ofpolyvinylpyrrolidone, polyacrylic acid, and silicone.

In an embodiment, the inner conductor and outer shield can beelectrically coupled to an interface. In an embodiment, the interfacecan include at least one of a tuning-matching circuit, a balun circuit,a decoupling circuit, and a variable capacitor. In an embodiment, theinterface can couple to an MRI scanner.

In an embodiment, the biopsy or sample needle antenna can receivemagnetic resonance spectroscopy information from a sample. Magneticresonance spectroscopy information can include, e.g., information frommagnetic nuclei, such as hydrogen, phosphorus, sodium, and other knownin the art. When a one-dimensional MR Spectroscopy technique along thelength of the antenna is utilized, very high resolution spectroscopy ofthe tissue around the needle can be obtained. The antenna signalreception characteristics can facilitate localization, particularly inthe radial direction. One use of a biopsy device disclosed herein isaccurate localization of malignant tumors by using MR spectroscopy. Itis known that at least some biopsy techniques have very high specificitybut low sensitivity. On the other hand, some tumors may not be visibleby hydrogen (proton) MRI, however proton or other nuclei, (such as Na,P, Ca etc) spectroscopy information may reveal signal that candifferentiate the malignant tumor from the normal and the benign tumor.With the aid of the MR spectroscopy guidance, sensitivity of the biopsyprocedure can be increased by placing the needle in the tumor withsuspected malignancy.

In an embodiment, the antenna can include a cannula including an outershield, an obturator including an inner conductor, the obturatorslideably displaceable relative to the cannula, and an insulatorelectrically insulating the outer shield from the inner conductor.

In an embodiment, coupling can include trapping the biopsy between thecannula and the obturator. In an embodiment, trapping can include movingat least one of the cannula and the obturator relative to the other. Anembodiment can further include coupling the magnetic resonance data toan MRI scanner to form a magnetic resonance image.

An embodiment provides a device that can be used as a biopsy or sampleneedle in MR-guided core biopsy procedures, as well as function as an MRantenna for accurate needle positioning and high-resolution imaging ofthe target. Such a device may have application in a number of MRI-guideddiagnostic procedures to evaluate pathologic lesions including cancers,to assess the health of various organs in the body, and to provideinformation useful for assessing therapeutic response.

Systems and methods are disclosed to enhance and facilitate theperformance of biopsy procedures with MRI.

In an embodiment, a biopsy device is MRI compatible.

In an embodiment, a biopsy device can be easily visualized and/ortracked by MRI.

An embodiment can facilitate high resolution imaging of a target area.

In an embodiment, a biopsy device permits sampling and collection oftissues and/or fluids under MRI guidance.

An embodiment provides an image-guided biopsy that obviates the need forbiopsy needles that can generate visible artifacts for needlelocalization.

An embodiment provides a method to perform MRI-guided biopsy procedures.

An embodiment provides a system to perform MRI-guided biopsy procedures.

An embodiment provides for an MRI-compatible device that includes abiopsy needle, means for sampling and collection of tissue and fluidsamples, and an antenna for receiving MRI signals. High resolutionimaging of target lesions and tissues is rendered by virtue of the closeproximity of the MRI antenna to the tissue of interest.

In an embodiment, an image may be a composite image.

An embodiment provides a device with an insulated movable obturator,which has a cutting edge that slices the tissue on the slide-slitportion and thus performs the biopsy procedure, collecting the tissuesamples. The obturator also forms the inner conductor of a looplessantenna type detector (as described by Ocali and Atalar, cited above).In addition, the device is provided with a cannula, which, inconjunction with a mechanical spring assembly that is electricallyconnected to the cannula, effectively serves as the outer RF shieldportion of the loopless antenna. The biopsy needle is charged, bydrawing the plunger in the proximal direction. The MRI antenna receiverfunction is preferably performed with the biopsy needle charged and theobturator is pushed into the cannula.

In an embodiment, the biopsy needle MRI detector device is connected tocircuitry that provides for decoupling of the antenna during MRIexcitation, and for matching and tuning of the MRI antenna in order toenhance and maximize MRI performance. It also functions to connect theneedle to an MRI scanner.

In an embodiment, a MRI-compatible biopsy needle device with MRIreceiving antenna is combined with matching tuning and decouplingcircuitry and an MRI scanner to guide, perform, and providevisualization of biopsy procedures.

An embodiment provides a method of performing an image-guided biopsyemploying the MRI-compatible biopsy needle device with MRI receivingantenna, matching tuning and decoupling circuitry, in conjunction withan MRI scanner. The method provides for accurate needle positioning andhigh resolution imaging of target pathologic lesions and nearby tissues,thereby enabling avoidance of injury to critical areas as the device isintroduced, and providing improved tissue characterization andmorphologic information about suspected lesions and pathologies. Thiswill facilitate potential medical interventions such as surgicalplanning, increase the accuracy of the biopsy procedure, and avoidunnecessary repeated biopsies.

An embodiment provides an MRI-compatible biopsy needle modified to forma loopless MRI antenna. The needle has a moveable cannula with a cuttingedge that provides sample collection for subsequent removal andhistological analysis. The needle device is interfaced to decoupling,matching and tuning circuit and connected to the receiver input of anMRI scanner, to permit images to be created from the MRI signals therebydetected. The images are used to guide the introduction and ingress ofthe biopsy needle into a subject positioned in the MRI scanner, for thepurpose of providing accurate targeting of the biopsy site, and detailedimaging of the surrounding local anatomy for assessment.

In an embodiment, a method of MRI imaging includes positioning aspecimen within a main magnetic field, introducing an antenna in closeproximity to the specimen, employing as the antenna a loopless antenna,imposing the main magnetic field on a region of interest of thespecimen, applying radio frequency pulses to the region of interest toexcite magnetic resonance signals within the specimen, applying gradientmagnetic pulses to the region of interest to spatially encode themagnetic resonance signals with the antenna receiving the magneticresonance signals and emitting responsive output signals, employingprocessing means for receiving and processing the responsive outputsignals and converting them into magnetic resonance information, andemploying display means for receiving the magnetic resonance informationfrom the processing means and displaying the same as an image or aschemical shift spectra.

The antenna employed in one preferred embodiment has the looplessantenna and a coaxial cable means structured to be received within theintravascular system, the pancreatic duct, or a tortuous passageway of apatient.

The antenna employed in another preferred embodiment is a looplessantenna structured as a biopsy needle.

The antenna employed in another preferred embodiment has a balancingtransformer means operatively associated with a portion of the outershield of a coaxial cable. For applications within a blood vessel, aninsulator in the balancing transformer is preferably employed with adielectric constant about equal to a dielectric constant of blood in theblood vessel.

The antenna employed in another preferred embodiment has an impedancematching circuit electrically interposed between the loopless antennaand the processing means to enhance radio frequency power transfer andmagnetic resonance signal-to-noise ratio from the loopless antenna tothe processing means.

The antenna for most embodiments is preferably flexible so as to permitefficient movement through specimen passageways and other specimens orsamples to be analyzed regardless of whether the path is straight ornot.

The antenna may be employed in chemical shift imaging throughacquisition of spatially localized chemical shift information.

In this manner, the method enables both imaging and chemical shiftanalysis which may also be advantageously employed substantiallysimultaneously with surgical intervention.

A dipole antenna portion of the loopless antenna may be on the order ofabout 3 cm to about 20 cm in length, and may have a relatively smallmaximum outer diameter of about 0.3 mm to about 1.0 cm.

In one embodiment, the antenna also functions as a transmitting antennato provide the RF signals and, thereby, provide enhanced efficiency ofoperation for certain uses.

The method may also employ additional elements, such as a balancingtransformer and/or an impedance matching circuit in order to provideenhanced operation.

A corresponding magnetic resonance analysis apparatus is provided.

A corresponding magnetic resonance antenna assembly includes an antennahaving loopless antenna means at least for receiving magnetic resonancesignals emitted from a specimen and emitting responsive output signals.

Disclosed systems and methods can facilitate providing high-resolutionand spectroscopic imaging of the interior of specimens, including invivo and in vitro imaging of patients and patient derived specimens orsamples.

Disclosed systems and methods can facilitate rapid imaging of walls ofsmall, tortuous blood vessels with high-resolution, as well as otherspecimens, and will permit the use of multislice data acquisitiontechniques.

Disclosed systems and methods can facilitate acquiring imagessimultaneously with surgical procedures such as removing plaque fromblood vessels.

An embodiment includes a loopless, flexible antenna that can provideboth qualitative and quantitative data and to facilitate use of the samesubstantially simultaneously with medical intervention to correctundesired conditions.

An embodiment facilitates acquiring morphological information about softtissue and plaque.

An embodiment facilitates acquiring chemical information about softtissue and plaque.

In an embodiment, the antenna may function only as a receiver antenna ormay function as an antenna for both excitation and detection of MRsignals.

In an embodiment, the antenna may function as an invasive probe, such asa catheter.

In an embodiment, the antenna may function as a probe-type medicaldevice such as a biopsy needle.

In an embodiment, no tuning or impedance matching circuit is generallyrequired.

In an embodiment, no tuning of the antenna is generally required aftersuch antenna is inserted in a patient.

An embodiment can include or couple to an impedance matching circuitwhich may be employed with conventional hardware.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of a magnetic resonance analysissystem.

FIG. 2 is a form of a catheter coil for the system of FIG. 1.

FIG. 3 is a schematic of a loopless antenna and an impedance matchingcircuit for the system of FIG. 1.

FIG. 4 is a cross-sectional view of a loopless balanced antenna.

FIGS. 5A–5B are plots of noise resistance with respect to antenna lengthfor a loopless antenna similar to the embodiment of FIG. 4.

FIG. 6 is a schematic illustration of the loopless antenna of FIG. 4, animpedance matching and decoupling circuit, and a preamplifier.

FIG. 7 is a schematic illustration of the loopless antenna of FIG. 4, amatching circuit, two coaxial cables, and a transceiver.

FIG. 8 is a cross-sectional view of a loopless antenna and coaxial cablepositioned in a blood vessel.

FIG. 9 is a cross-sectional view of a human pancreas with a catheterloopless antenna positioned in the pancreatic duct.

FIG. 10 is a log-log plot of measured and theoretical signal-to-noiseratio with respect to radial distance from the loopless antenna of FIG.4.

FIG. 11 is a contour plot of theoretical SNR as calculated for abalanced loopless antenna.

FIG. 12 is a schematic cross-sectional illustration showing a looplessantenna employed as a biopsy needle.

FIG. 13 is a representation of the spectra of three adjacent voxelsalong the length of the catheter coil of FIG. 2.

FIG. 14 is a cross-sectional view of another embodiment of a dipoleantenna.

FIG. 15 is a schematic illustration of a loopless antenna employed incombination with a catheter coil.

FIG. 16 shows a schematic diagram of a needle antenna and decouplingmatching and tuning circuitry.

FIG. 17 shows a schematic diagram of the electrical connections to theproximal end of the biopsy-needle-antenna.

FIGS. 18 and 19 depict two exemplary positions that a biopsy needle canadopt.

FIG. 20 shows a diagram of an obturator of a biopsy needle antenna.

FIG. 21 shows a block diagram illustrating the operation of an MRIscanner system.

FIGS. 22A and 22B show images acquired with a biopsy needle antenna.

FIGS. 23A–F depict a sequence of images from an image-guided biopsyprocedure.

DESCRIPTION

MRI-guided biopsies performed with non-magnetic devices using free-handor stereotaxy techniques have been reported (see for example, S. G.Silverman et al., Radiology, 197:175–181, 1995; J. S. Lewin et al., AJRAm J Roentgenol 166:1337–1345,1996). These procedures also use artifactsgenerated by the needle for localization, and typically require the useof external MRI detection coils to determine the needle position and thetarget. Other needle designs, either coated or not coated with MRIdetectable substances and manufactured from non-magnetic materials andappropriately protected from induced heating, can avoid MRI artifacts.However, even though such devices are MRI-compatible, because they arenot deployed as MRI antennas themselves, they cannot contribute to MRIperformance nor enable high-resolution MRI of the target area.

MRI signals are weak and the ability of an antenna to detect themdepends on both the antenna size and its proximity to the source ofthose signals. Thus, in order to improve the MRI signal, an MRI antennamay be placed near or inside the subject to be imaged. Such improvementscan enable valuable increases in resolution sensitivity of a targetarea, reduction in scan time, and provide evidence of the MRI antennaitself on the MRI. For example, long, flexible loop antennas producelocal regions of high signal permitting high resolution MRI in theirvicinity when implemented as an internal MRI antenna, as shown forexample by Atalar E, Bottomley P A, Ocali O, Correia L C, Kelemen M D,Lima J A, Zerhouni E A, “High resolution intravascular MRI and MRS byusing a catheter receiver coil”, Magn Reson Med. 1996;36:596–605. Theloopless antenna design of Ocali O and Atalar E (“Intravascular magneticresonance imaging using a loopless catheter antenna” in Magn Reson Med.1997;37:112–8) may also be deployed as an internal MRI antenna torealize important resolution and sensitivity advantages.

By providing the ability both to visualize where on the image theantenna is located, and to provide high sensitivity and ahigh-resolution imaging capability an MRI scanner equipped with suchdetectors could be advantageous in medical procedures where MRI is usedsimultaneously to track the position of an interventional device, and toprovide a way of evaluating the structures surrounding the device. Inparticular, by developing MRI-compatible needle biopsy and/or needleinterventional devices that incorporate an MRI antenna capability,needle biopsies and/or interventions could be performed under MRIguidance with the following important advantages over X-ray andultrasound-guided needle techniques: (1) full 3D anatomicalvisualization of the organ or tissue of interest during the examination;(2) an ability to image in any plane or orientation; (3) MRI has muchgreater sensitivity to soft tissue and pathology, enabling superiorcharacterization of pathologic features of a target region; (4) theability to obtain diverse functional information about the target organor tissue via one or more of the many available state-of-the-art MRItechniques; (5) MRI involves zero exposure to potentially damaging x-rayradiation; and (6) because localization is determined by thesuper-position of magnetic fields to which the body is transparent to,and not by beams, there are no beam diffraction and reflectionartifacts, nor (7) problems with opacity or imaging though bone etc.

FIG. 1 shows a schematic representation of the general concept ofmagnetic resonance analysis as employed with a specimen. An RF source 2provides pulsed radio frequency energy to the specimen to excite MRsignals therefrom. The specimen, in the form shown, is a patient 4disposed in the main magnetic field which is created by a magnetic fieldgenerator 6. The generator 6 includes a magnetic field gradientgenerator for establishing gradients in the main magnetic field byapplying gradient magnetic pulses on the region of interest of thepatient 4 in order to spatially encode the MR signals.

The exemplary patient 4 is generally aligned with the main magneticfield and the RF pulses are emitted perpendicular thereto to oneportion, several portions, or all of the specimen. Where oblique imagingis employed, the angle of impingement of the vector representing thespatial gradient of the magnetic field will be angularly offset fromeither the x, y, or z directions (not shown). This arrangement resultsin excitation of the nuclei within the area or volume to be imaged andcauses responsive emission of magnetic energy which is picked up by areceiver 8 having a loop antenna (i.e., a receiver coil) in closeproximity to the patient 4.

Preferably, the loop antenna of the receiver 8 is aligned with the zdirection (i.e., the direction of the main magnetic field) in order tohave maximum sensitivity. In the event the loop antenna is perpendicularto the main magnetic field, it has a practically zero sensitivity atcertain locations. For oblique angles therebetween, the loop antenna hasdata acquisition capability, albeit with reduced sensitivity, therebypermitting data acquisition even at oblique angles.

The loop antenna or receiver coil of the receiver 8 has a voltageinduced in it as a result of such responsive emissions of magneticenergy. As a practical matter, separate coils or identical coils may beemployed by the RF source 2 and receiver 8. The responsive output signalemerging from receiver 8 is amplified, phase-sensitive detected, andpasses through analog-to-digital (A/D) converter 10 and enters aprocessor, such as computer 12, which receives and processes the signalsfrom the converter 10 and creates MR information related thereto. Withincomputer 12 the Fourier Transformations of signals convert the plot ofamplitude versus time to a map of the distribution of frequencies byplotting amplitude versus frequency. The Fourier Transformations areperformed in order to establish the intensity value locations ofspecific image pixels of the specimen and to obtain chemical shiftspectra at those locations. These values may be stored, enhanced orotherwise processed, and emerge to be received and displayed as an imageor as chemical shift spectra, as appropriate, on a suitable screen, suchas a cathode-ray tube (CRT) 16, for example.

In chemical shift spectra applications, for example, the magnetic fieldgradient generator of generator 6 generates the magnetic field gradientsubstantially parallel to the loop antenna of the receiver 8 over theregion of interest in order to generate one-dimensional resolvedchemical shift spectra which are spatially resolved substantially alongthe length of the loop antenna on the region of interest. The computer12 converts spatially localized chemical shift information in theresponsive output signals to chemical shift spectra, and employs the CRT16 to receive and display such spectra. This facilitates one-dimensionalchemical shift imaging in which the chemical shift information isspatially resolved in a direction substantially along the length of theloop antenna on the region of interest of the specimen.

Those skilled in the art will appreciate that the transmissionproperties of a coil may be used to analyze its reception properties.Referring to FIG. 2, in general, the signal voltage V_(S) of a coil 18is determined in Equation 1:V _(S) =ωμ{right arrow over (H)}·{right arrow over (M)}  (Eq. 1)wherein ω is 2πF, F is frequency of RF source 2, μ is permeabilityconstant, {right arrow over (H)} is magnetic field (vector) generated bycoil 18 at unit input current I, and {right arrow over (M)} is samplemagnetization (vector). Of the factors affecting the signal voltageV_(S), H is the only coil-dependent parameter.

The RMS noise voltage V_(N) of the coil 18 is determined in Equation 2:V _(N)=√{square root over (4k _(B) TRf)}  (Eq. 2)wherein k_(B) is the Boltzman constant, T is sample temperature, R isreal part of impedance seen from the terminals of coil 18,f=2BW/(N_(x)N_(y)NEX) is effective pixel bandwidth, BW is receiverbandwidth, N_(x) is number of pixels along the readout direction, N_(y)is number of pixels along the phase encoding direction, and NEX isnumber of averages. The only coil-dependent parameter that affects thenoise voltage V_(N) is R.

The signal-to-noise ratio (SNR) is determined in Equation 3:

$\begin{matrix}{{SNR} = {\frac{V_{S}}{V_{N}} \propto \frac{H}{\sqrt{R}}}} & \text{(Eq.~~3)}\end{matrix}$wherein, H is magnetic field (value) generated by coil 18 at unit inputcurrent I. To improve SNR, H should increase and R should decrease. Forexample, in coils, these are generally conflicting goals. A typicalvalue of R for the coil 18 is about 0.5Ω.

In the structure of the conventional catheter coil 18, magnetic fieldsgenerated by the two conductors 19, 20 cancel partially. Thiscancellation effect becomes more pronounced as the distance of thespecimen from the coil 18 increases. In this configuration, the path ofthe current I is completed by the end conductor 21, which forms anelectrical loop or coil with the conductors 19, 20. The performance ofthe coil 18 depends strongly on the separation distance d between theconductors 19, 20 and worsens (improves) as such separation decreases(increases).

FIG. 3 illustrates an antenna 22. The cancellation of the magneticfields is avoided by separating the conductors 24, 26 as schematicallyshown in FIG. 3. The H field increases considerably by this operation.In this configuration, the path of the current I′ is not completed, andcharges simply oscillate between the two tips of the antenna 22. The Hfield generated by the antenna 22 becomes circular thereabout and isapproximately inversely proportional with the distance thereto. Theantenna 22 includes the conductors 24,26, which form a loopless antenna27′ having a dipole antenna portion 28′ and a connection portion 29′;and, in this embodiment, an impedance matching circuit 30. The impedancematching circuit 30 is electrically interposed between the looplessantenna 27′ and a preamplifier 68 of the receiver 8 of FIG. 1 andenhances RF power transfer and MR SNR from the antenna 27′ to theconverter 10 of FIG. 1. The parameters of the impedance matching circuit30 are chosen to resonate the antenna 27′ at the MR frequency of thenuclei of interest and to match the antenna 27′ to the optimum inputimpedance of the preamplifier 68.

EXAMPLE 1

FIG. 4 is a cross-sectional view of an exemplary loopless balancedantenna 27. A dipole antenna portion 28 receives MR signals emitted froma specimen responsive to pulsed RF signals and emits responsive outputsignals. A connection portion 29 emits the responsive output signals tothe impedance matching circuit 30 of FIG. 3. In this embodiment, theconnection portion 29 is a coaxial cable having an outer primary shield31 and an inner conductor 32. The coaxial cable 29 is electricallyinterposed between the dipole antenna portion 28 and the impedancematching circuit 30.

The dipole antenna portion 28 has a first pole 33 and a second pole 34.A portion 36 of the outer shield 31 is operatively associated with thefirst pole 33. A portion 38 of the inner conductor 32 is operativelyassociated with the second pole 34. The second pole 34 preferablyincludes a cylindrical conductor 40 electrically interconnected with theportion 38 of the inner conductor 32.

The portion 36 of the outer shield 31 at the first pole 33 forms aninner primary shield 42 and an outer secondary shield 44, each of whichis coaxial with the inner conductor 32. The first pole 33 includes theshields 42, 44. In this manner, the secondary shield 44 is also forreceiving the MR signals.

The first pole 33 also includes a dielectric coating or insulator 46under the outer secondary shield 44, between such shield 44 and theinner primary shield 42. The insulator 46 and the shields 42, 44 form abalancing transformer operatively associated with the first pole 33. Thebalancing transformer suitably disables current flow on the outersurface of the primary shield 31, without significantly impeding currentflow on the inner surface thereof.

Preferably, the insulator 46 is a relatively high dielectric constant(∈_(r)) insulator having a value of about 70 to about 100. Preferably,for optimal balancing, the dielectric constant of the insulator 46 isselected in order that the length L/2 (as shown in FIG. 3) of thetransmission line formed by the primary shield 42 and the secondaryshield 44 (as shown in FIG. 4) has a length of λ/4, where λ is thewavelength in the insulator 46 at the MR frequency of nuclei ofinterest. In this manner, the unbalanced current flowing on the outersurface of the primary shield 31 is greatly reduced.

For applications in vivo in a patient, the ∈_(r) value of the insulator46 is preferably selected to match the ∈_(r) value of the surroundingmedium 47 (e.g., the ∈_(r) value of blood which ranges from about 70 toabout 100). For other applications, the antenna 27 is preferablyintroduced in close proximity to the specimen. The insulator 46 may bemade of any insulator having a suitable ∈_(r) value and, preferably, ismade of titanium oxide or a composite thereof.

Preferably, in terms of extending the sensitivity along the length of aloopless antenna, as discussed below in connection with FIG. 8, abalancing transformer is not employed. In the embodiment of FIG. 8,current flows on the outer surface of the primary shield 31 and thenoise voltage is higher thereby providing a lower SNR. The primaryshield 31 serves to receive the MR signal as well as the portion of thepole 86 which is adjacent the pole 88. However, removing the balancingtransformer reduces the SNR slightly.

The balancing transformer of FIG. 4 is preferably employed to avoidunbalanced currents which would otherwise make the input impedanceZ_(IN) of FIG. 3 sensitive to changes in loading conditions and theposition of the loopless antenna 27.

The inner conductor 32 and the cylindrical conductor 40 may be made of agood non-magnetic, electrical conductor, such as copper, silver, or skineffect, however, wherein only about an 8 μm outer layer of theconductors 32, 40 carries electrons at RF frequencies, a material platedwith a good conductor will also function effectively. For example,silver plated copper, gold plated copper, or platinum plated copper maybe employed.

The dipole antenna portion 28 of the exemplary balanced loopless antenna27 has a length L of about 3 cm to about 20 cm, with larger (smaller)lengths obtained with smaller (larger) RF frequencies (e.g., less thanabout 400 MHz), although larger lengths of up to about 2 m are possiblewith the unbalanced loopless antenna 74 of FIG. 8. The length Lfacilitates multislice imaging without moving the loopless antenna 27.Preferably, resiliently flexible loopless antennas 27, 74 are provided.The optimal length of the antenna 27 at 1.5 T in human tissue is about 7cm to about 10 cm. The exemplary balanced loopless antenna 27 has amaximum width W (FIG. 4) of about 0.5 mm to about 1.0 cm, althoughsmaller widths of about 0.3 mm are possible with the unbalanced looplessantenna 74 of FIG. 8.

The sensitivity profile of the exemplary antennas 27, 74 depends on therespective antenna's orientation with respect to the main magneticfield. The best performance is achieved when the antennas 27, 74 arealigned with the main magnetic field. In other words, in order tofunction effectively, the longitudinal axis 48 is parallel to the mainmagnetic field B (FIGS. 4 and 8) with the poles 33, 34 along the lengthof the loopless antenna 27. For example, for in vivo applications of theantennas 27, 74, the patient (and, hence, the antenna therein), may bemoved to provide suitable alignment with the direction of the mainmagnetic field B.

The antennas 27, 74 supply a relatively high signal voltage, since thereare no magnetic field cancellations as in the coil 18 of FIG. 2. Toestimate SNR performance, as shown in Equation 3, the noise resistance R(i.e., the real part of the impedance Z_(IN)) is necessary. The inputimpedance Z_(IN) of the antennas 27, 74 may be measured experimentally(e.g., using a vector impedance meter in a saline solution which hasconductivity similar to the particular specimen such as mammaliantissue). It is also possible to calculate the input impedance Z_(IN) bysolving the associated electromagnetic problem. Both the real (R) andimaginary (jX) parts of the input impedance Z_(IN) are preferablyemployed in designing the impedance matching circuit 30 of FIG. 3.

Preferably, for optimal SNR performance, the noise resistance R shouldbe as small as possible. As shown in FIGS. 5A and 5B, noise resistance R(ohms) is plotted for changing antenna length (meters), for twodifferent exemplary main magnetic field strengths, 4.7 Tesla (T) and 1.5T, respectively, for a loopless antenna (not shown) similar to theloopless antenna 27 of FIG. 4. The loopless antenna represented by FIGS.5A and 5B has a diameter of about 1.0 mm and a balancing transformerinsulator with a dielectric constant (∈_(r)) representative of humanbody tissue. In both cases, R attains a shallow minimum (e.g., about 20Ωto about 30Ω). Preferably, the length of the loopless antenna is chosenaround those minima.

The noise resistance R of the antenna 22 of FIG. 3 weakly depends on theradius of the conductors 24, 26. Compared to a typical 0.5Ω inputimpedance of the conventional coil 18 of FIG. 2, the noise resistance Rof the loopless antenna 27 of FIG. 4 approaches about two orders ofmagnitude larger and, hence, the noise voltage V_(N) approaches aboutone order of magnitude larger (as shown by the square root function ofEquation 2). However, the signal voltage V_(S) of the loopless antenna27 is also larger. The SNR performances of the coil 18 and the looplessantenna 27 equate at a distance of about 5–8 times the conductorseparation distance d for the coil 18. At smaller distances, the coil 18is better, but for larger distances the loopless antenna 27 has a betterSNR performance.

EXAMPLE 2

FIG. 6 is a schematic illustration of the loopless antenna 27 of FIG. 4,and a suitable exemplary impedance matching and decoupling circuit 50,although the disclosed systems and methods are applicable to a widevariety of impedance matching circuits, and tuning and impedancematching circuits. The loopless antenna 27 is electricallyinterconnected to the circuit 50 by the coaxial cable 29. The circuit 50serves to match the impedance of the loopless antenna 27 with thecharacteristic impedance Z₀ of a coaxial cable 51. The coaxial cable 51is connected to the preamplifier 68 of the receiver 8 of FIG. 1 andcarries the MR signal thereto. In this manner, the coaxial cable 51 iselectrically interposed between the computer 12 of FIG. 1 and thecircuit 50, with such circuit 50 matching the input impedance Z_(IN) ofthe loopless antenna 27 to the characteristic impedance Z₀ of the cable51.

The loopless antenna 27 has a relatively large noise resistance R, whichmakes it possible to place the circuit 50 relatively far from theantenna 27 without significant SNR performance degradation. This is animportant advantage over the relatively low noise resistance coil 18 ofFIG. 2 because, during imaging therewith, the matching circuitry (notshown) thereof is preferably placed inside the specimen to eliminate asignificant SNR loss.

The circuit 50 includes a direct current (DC) blocking capacitor 52, amatching capacitor 54, and a PIN diode 56. The matching capacitor 54 iselectrically interposed in the circuit 50 between the inner conductor 32and the outer shield 31 of the coaxial cable 29. The PIN diode 56 iselectrically interposed between the DC blocking capacitor 52 and thepreamplifier 68. The DC blocking capacitor 52 is electrically interposedbetween the PIN diode 56 and the inner conductor 32 of the coaxial cable29. The coaxial cable 29 is preferably structured with a suitablediameter for reception within an intravascular system, whereas thecircuit 50 and the coaxial cable 51 may have a larger diameter, althoughthe disclosed systems and methods are applicable to a wide variety ofimpedance matching circuits (e.g., formed from individual discretecomponents, electronic integrated circuits, other miniaturizedcircuits).

In receive only mode during RF excitation, RF current may be induced inthe antenna 27. In order to resist current induction in the antenna 27during RF transmission, and obviate resonance of the antenna 27 whichmay interfere with the flip angle profile, the MR scanner hardware inthe RF source 2 of FIG. 1 may provide a positive DC pulse to the antenna27 for this purpose. The positive DC pulse turns on the PIN diode 56during RF transmission.

In the exemplary circuit 50, L₁ is the distance between PIN diode 56 andthe matching capacitor 54, and L₂ is the distance between matchingcapacitor 54 and the point 58 (best shown in FIG. 4) intermediate thepoles 33,34 of the loopless antenna 27. The capacitance (C₂) of thematching capacitor 54 and the length L₂ are chosen such that the inputimpedance Z_(IN) of the loopless antenna 27 is equal to thecharacteristic impedance Z₀ of the coaxial cable 51. In other words, thelength L₂ is adjusted in order that when the PIN diode 56 is on, thecoaxial cable 29 behaves like an inductor and resonates with thecapacitor 54 to disable a current through the loopless antenna 27,although various designs are possible to achieve this desiredperformance. Then, the length L₁ is chosen such that when the PIN diode56 is turned on, the impedance, Z₁, seen by the loopless antenna 27,becomes as large as possible.

In the exemplary embodiment, a substantial portion (i.e., coaxial cable29) of the length L₂ may be inserted within the specimen with thecircuit 50 external thereto. The exemplary circuit 50 includes a coaxialcable 60 having a center conductor 62 and outer shield 64. The matchingcapacitor 54 is electrically interconnected between the center conductor62 and outer shield 64 at one end of the coaxial cable 60. The DCblocking capacitor 52 is electrically disposed at the other end betweenthe center conductor 62 and the PIN diode 56.

For example, with tap water as the medium, the values of the designparameters are: the capacitance (C₁) of the DC blocking capacitor 52 isabout 500 pF, C₂ is about 70 pF, L₁ is about 0.06λ, L₂ is about 0.209λ,and Z₀ is about 50Ω, with λ being about 2 times the length L of FIG. 4.Regardless of these values, the performance of the circuit 50 isgenerally not critical since the input impedance Z_(IN) of the looplessantenna 27 is typically of the same order of magnitude as thecharacteristic impedance of the coaxial cable 51.

An example of an MR scanner usable in the practice of the disclosedsystems and methods is the General Electric (G.E.) 1.5 T Signa™ MRscanner, although the disclosed systems and methods are applicable to awide variety of MR scanners having a wide range of main magnetic fieldstrengths. The MR scanner sources RF pulses to a transmitting coil whichtransmits such RF pulses in order to excite MR signals. As discussedbelow in connection with FIG. 7, the loopless antenna 27 may also beemployed as an RF pulse transmitting source in addition to employment asa receiver antenna.

Preferably, to obviate insertion of any active or passive electroniccomponents in a blood vessel, a λ/2 cable length, or multiple thereof,is added to the length L₂. In this manner, the length of the coaxialcable 29 may be extended by up to about several feet to facilitate MRanalysis more deeply within the specimen.

EXAMPLE 3

FIG. 7 is a schematic illustration of the loopless antenna 27, thecoaxial cable 29, an impedance matching circuit 66, the coaxial cable51, and a transceiver 69. The receiver (RX) portion of the transceiver69, through the switch portion 70 thereof, is employed to receive theresponsive output signals from the loopless antenna 27. For matching atthe time of manufacture, matching circuit 66 is provided with capacitors71, 72, which are electrically interconnected to the loopless antenna 27by the coaxial cable 29. The matching circuit 66 maximizes RF powertransfer from the antenna 27 to the RX portion of the transceiver 69which receives and amplifies the output of the circuit 66. In thisembodiment, unlike the embodiment of FIG. 6, there is no PIN diode andthe loopless antenna 27 provides a transmitter antenna function as wellas a receiver antenna function. The transmitter (TX) portion of thetransceiver 69, through the switch portion 70 thereof, is employed totransmit the RF pulses to loopless antenna 27.

The matching circuit 66 is preferably placed nearby the loopless antenna27, although the length of the coaxial cable 29 may be extended up toabout several feet in a similar manner as discussed above in connectionwith FIG. 6. This is especially advantageous in the case where theloopless antenna 27 and the coaxial cable 29 are employed in the mannerof a catheter in vivo. The arrangement of the impedance matching circuit66 in FIG. 7 is not limiting and it will be understood that otherimpedance matching, tuning and impedance matching, or impedance matchingand decoupling arrangements (e.g., inductor/capacitor, a circuit forshorting the coaxial cable, suitable RF switching circuitry, a coaxialcable having an impedance about equal to the impedance of the looplessantenna) will be evident to those skilled in the art.

EXAMPLE 4

FIG. 8 is a cross-sectional view of a loopless antenna 74 and a coaxialcable 29″ positioned in an intravascular system such as, for example,within a blood vessel such as a human vein 76. The vein 76 has aninterior bore 78 filled with blood 80, and one or more atheroscleroticplaque deposits, such as plaque deposits 82, which are secured to theinterior surface 84 of the vein 76. The antenna 74, in the form shown,is connected to the coaxial cable 29″ which, in turn, is connected to asuitable circuit, such as the circuit 50 of FIG. 6 or the circuit 66 ofFIG. 7, which serves to match the impedance of the antenna 74 with theimpedance of the coaxial cable 51 of FIGS. 6 and 7.

The loopless antenna 74 has a first pole 86 and a second pole 88. Thecylindrical outer shield 31 of the coaxial cable 29″ is electricallyinsulated from the center conductor 32 of such cable 29″ by thedielectric portion 92 thereof. Unlike the antenna 27 of FIG. 4, theantenna 74 does not have a balancing transformer insulator such asinsulator 46.

The second pole 88 includes a cylindrical conductor 94 electricallyinterconnected with the portion 38 of the inner conductor 32.Preferably, for use in a patient, the end 96 of the cylindricalconductor 94 is suitably rounded to obviate damaging the patient (e.g.,the interior surface 84 of the vein 76). In this application, theloopless antenna 74 and coaxial cable 29″ are employed in the manner ofan invasive probe, such as a catheter, with the matching circuit, suchas the circuit 50 of FIG. 6 or the circuit 66 of FIG. 7, locatedexternal to the vein 76. The exemplary loopless antenna 74 and coaxialcable 29″ are elongated along longitudinal axis 97 with a length of upto about 2 m and an external diameter of about 0.3 mm in order to bereceived within a blood vessel of a patient.

The antenna 74, cable 29″ and suitable matching circuit (not shown) areemployable to acquire MR image information or MR chemical shiftinformation about atherosclerotic plaques. For example, as discussedabove in connection with FIG. 1, the computer 12 converts the responsiveoutput signals from the antenna 74 into MR image information, and theCRT 16 displays the MR image information in order to image the vein 76.It will be appreciated that the cylindrical conductor 94 mayalternatively be employed with the antenna 27 of FIG. 4 for highresolution intravascular and other in vivo applications in a patient. Itwill further be appreciated that the use of the exemplary antenna 74 andcable 29″ may be employed generally simultaneous with a medical,surgical, or interventional procedure on the patient, such as removal ofthe plaque deposits 82 from the vein 76 by a suitable cutting device(not shown).

Insulating the antenna 74 does not change its electrical propertiesunless the insulation (not shown) is extensively thick (e.g., greaterthan about 0.1 mm).

It will be appreciated that the antennas 27 and 74 of FIGS. 4 and 8,respectively, may be employed, for example, in a blood vessel to providean image and 1-D spectroscopic analysis of plaque built up on theinterior of the vessel wall with multislice imaging being provided in anefficient manner due to such elongated antennas being employed. Theantennas 27, 74 may also be employed to examine many othercharacteristics, such as fatty streaks, calcification, sclerosis, andthrombosis, for example. It will further be appreciated thatsubstantially simultaneously with the use of such antennas and coaxialcables 29, 29″, medical intervention as, for example, by laser therapyor destruction of the undesired plaque, may be employed. Similarly, anynormal diagnostic or therapeutic measures undertaken with the aid of anendoscope (not shown), may be accomplished substantially simultaneouslywith the use of such antennas for imaging and/or spectroscopic analysis.

EXAMPLE 5

FIG. 9 is a cross-sectional view of a human pancreas 106 with theantenna 102 and a portion of the coaxial cable 104 positioned in apancreatic duct 108. An external dielectric material 100 may be employedas illustrated with the loopless antenna 102 and coaxial cable 104. Theantenna 102 and coaxial cable 104 are employed in the manner of aninvasive probe, such as a catheter, during a surgical procedure,associated with the pancreas 106, on the human patient. The antenna 102and coaxial cable 104 are introduced into the human patient to conductinternal MR analysis thereof.

The antenna 102 and cable 104 have an external diameter which isstructured to be received within a naturally occurring passageway in ahuman being, such as the opening 110 of the pancreatic duct 108. Thisopening 110, for example, is accessible during surgery on the duodenum112, although the antenna 102 and cable 104 are structured to bereceived within a wide variety of naturally open passageways (e.g., bileduct 114, urethra, ureter, esophagus, rectum, ear canal, nasal passage,bronchi, air passages) or man-made passageways in a patient. The antenna102 and cable 104 are flexible, whereby the same may assume a tortuouspath upon insertion into the pancreatic duct 108.

Preferably, the dielectric material 100 is resilient in order to permitflexing of the antenna 102 and cable 104, and return of the same totheir original configuration. Any suitable dielectric material havingthe properties required to function in this environment may be employed.In general, it is preferred that the antenna 102 and cable 104 becovered by about 5 to about 100 microns of such material. A suitabledielectric may, for example, be a bio-compatible plastic material, orblend having the desired properties. The dielectric material employedmay, for example, be tetrafluoroethylene, which is sold under the tradedesignation, “Teflon.” It is known for its fine electrical insulatingproperties, does not interact with any components in water, and can besafely used in blood vessels. The purpose of the dielectric material 100is to provide bio-compatibility. However, a relatively thick insulation(e.g., greater than about 0.1 mm) will improve SNR at the cost ofthickening the antenna 102 and cable 104.

It will be appreciated that the antenna 102, cable 104 and suitableimpedance matching circuit are employable with other specimens. Forexample, the image of the aorta of a live rabbit (not shown) may beobtained. The antenna 102 and cable 104 may be inserted from the femoralartery of the rabbit. Although the rabbit femoral artery is typicallyvery small (e.g., approximately about 1 mm in diameter), catheter-likeinsertion is easily performed with the exemplary antenna 102 and cable104.

Any suitable method, such as X-ray fluoroscopic imaging, may be employedto confirm the placement of the antenna 102 in the specimen. It will beappreciated that the placement of the antenna 102 may also be confirmedby a wide variety of other imaging methods. It will further beappreciated that the insertion of the antenna 102 into the patient maybe accomplished by direct insertion of the antenna 102 and cable 104into a suitable blood vessel, by insertion through a catheter guide, andby a wide variety of insertion methods.

FIG. 10 is a log-log plot of theoretical SNR (shown as a line 116) andmeasured SNR (shown as discrete diamonds 118) with respect to radialdistance from the longitudinal axis 48 of the antenna 27 of FIG. 4. Forexample, pulse sequences may be employed which allow a voxel size of0.16×0.16×1.5 mm. Images may be acquired with an 8 cm FOV, 512×512 dataacquisition matrix, 1.5 mm slice thickness, 2 NEX, and 16 KHz receiverbandwidth. Such imaging parameters correspond to an effective pixelbandwidth of 0.06 Hz and permit 12 slices of similar images to beobtained in about ten minutes.

The exemplary antenna 27 and cable 29 of FIG. 4, and suitable matchingcircuit provide a relatively high resolution of the specimen, such ashuman tissue, to a radial distance of about 10 mm from the longitudinalaxis 48, and can be employed to image to radial distances of about 20 mmor greater. Near-microscopic resolution can be obtained in the immediatevicinity of the antenna 27. Increasing the main magnetic field strengthimproves the resolution significantly and enables imaging with smallervoxel volume.

FIG. 11 is a contour plot of theoretical SNR as calculated for abalanced loopless antenna similar to the antenna 27 of FIG. 4. Thecalculation assumes that pulse sequences are employed at 1.5 T mainmagnetic field strength, with a 160×160×1500 micron voxel size and aneffective pixel bandwidth of 0.06 Hz. The units on the horizontal andvertical axes are in centimeters. The balanced loopless antenna issituated in the center of the plot at 0 cm of the horizontal axis andextends from −10 cm to 10 cm of the vertical axis.

EXAMPLE 6

FIG. 12 is a schematic cross-sectional illustration showing a looplessantenna 120 in the form of a biopsy needle 121. The antenna 120 isemployed in vivo on a patient 122. The body 123 of the patient 122contains a lesion 126. The antenna 120 serves to image the lesion 126 invivo before a sample 128 of the lesion 126 is taken by the biopsy needle121. This enables more accurate biopsy needle positioning. The antenna120 is formed at the end of a coaxial cable 130 having an outer shield132 and an inner conductor 134 which is electrically insulated from suchshield 132 by a dielectric portion 136. The biopsy needle 121 can slideinside a non-conducting sheath 138. The antenna 120 has a first pole 140formed by the shield 132, and a second pole 142 formed by the biopsyneedle 121 which is electrically connected to the portion 143 of theinner conductor 134, and which is electrically insulated from the shield132 by the dielectric portion 136. The antenna 120, coaxial cable 130and biopsy needle 121 are composed of materials which are magneticresonance compatible, such as a conductors or dielectric insulators asdistinguished from a steel material, for example. The end of the coaxialcable 130 opposite the biopsy needle 121 is preferably electricallyinterconnected with a suitable impedance matching circuit such as one ofthe circuits 50 and 66 of FIGS. 6 and 7, respectively.

FIG. 13 is a representation of the spectra of three adjacent voxelsalong the length of the catheter coil 18 of FIG. 2 which are establishedby the computer 12 of FIG. 1 to determine the chemical shift spectra atthose locations. It is believed that a comparable spectra may beacquired along the length of the loopless antenna 27 of FIG. 4. Thespectra of three adjacent voxels is shown in FIG. 13 with peaks146,148,150 representing water signals from the three regions and peaks152,154 from lipid signals in or adjacent to the region of interest,such as blood vessel walls. Water and lipid peaks will tend to varybetween normal and atherosclerotic vessels.

EXAMPLE 7

FIG. 14 is a cross-sectional view of a coaxial cable 29″ and a dipoleantenna 74′ similar to the loopless antenna 74 of FIG. 8. The dipoleantenna 74′ has a first pole 86 and a second pole 88′. The second pole88′ includes a mechanical loop conductor 94′ electrically interconnectedwith the portion 38 of the inner conductor 32. Preferably, for use in apatient, the end 96′ of the mechanical loop conductor 94′ is suitablyrounded to obviate damaging a patient (not shown). The exemplarymechanical loop conductor 94′ has a generally oval shape, although avariety of shapes are considered which are electrically isolated fromthe first pole 86. This is contrasted with the conventional cathetercoil 18 of FIG. 2 in which one of the conductors 19,20 may be connectedto a coaxial cable shield and the other conductor may be connected to acoaxial cable inner conductor, thereby forming an electrical loop.

EXAMPLE 8

FIG. 15 is a schematic illustration of the loopless antenna 27 employedin combination with the catheter coil 18 of FIG. 2. The conductor 19 ofthe catheter coil 18 is connected to outer shield 156 of coaxial cable158 and the conductor 20 is connected to inner conductor 160 therebyforming an electrical loop. Also referring to FIG. 1, the coaxial cable158 is connected to one preamplifier 68′ of the receiver 8. The coaxialcable 29 of the loopless antenna 27 is connected to another preamplifier68 of the receiver 8. Both the coil 18 and the antenna 27 receive MRsignals and emit corresponding output signals which are converted by theconverter 10 and are received and processed by the computer 12 in orderto combine the same into MR information for display by the CRT 16.Preferably, the coil 18 and the antenna 27 are mounted coaxially inorder to facilitate use of the better SNR performance of the coil 18 atrelatively small distances from the common axis and the better SNRperformance of the loopless antenna 27 at relatively large distancestherefrom. It will be appreciated that other types and number of coilsmay be employed with the preamplifier 68′ (e.g., two back-to-backsolenoid coils, a pair of quadrature coils) in combination with theantenna 27.

The exemplary antennas 27, 74, 120 disclosed herein increase SNR andprovide suitable resolution in MR imaging of blood vessels. Thesensitivity of the antennas 27, 74, 120 decays approximately as theinverse of the radial distance from the antenna longitudinal axis.Hence, it provides useful SNR in a cylindrical volume around suchantennas. The antennas 27, 74, 120 allow electronic circuits to beplaced outside the body and can be easily constructed to a very thindiameter which obviates the size and mechanical property restrictions ofcatheter coils. The physical dimensions of the antennas 27, 74 make itpractical for insertion into blood vessels. The antennas 27, 74, 120have a low quality factor (Q) and, hence, do not require appreciabletuning when inserted in non-linear intravascular systems.

The simple structure of the antennas 27, 74 makes it possible toconstruct and operate these devices in a reliable manner in variousimaging techniques, such as multislice MRI, 3-D MRI, or 1-Dspectroscopy, and in various interventional techniques on a wide varietyof specimens. The exemplary loopless antenna 120 and MR compatiblebiopsy needle 121 facilitate the same in addition to providing thecapability of conducting imaging before a biopsy sample is removed froma patient.

Pathogenesis of a blood vessel wall due to atherosclerosis is difficultto characterize by conventional techniques which only investigate thevascular lumen. Intravascular MRI has the unique potential tocharacterize all three layers of the vessel wall, plaque extent, andcomposition, as well as thickness and extent of the fibrous cap. Thegoal of high resolution imaging of atherosclerotic plaques can only beachieved by increasing the SNR of the acquired images. The exemplaryantennas 27, 74 greatly increase sensitivity to the target plaque.

The development of new MRI scanners has led to interventionalpossibilities which will benefit from the intravascular looplessantennas 27, 74. Interventional techniques for atherosclerotic diseasemay be monitored using real-time, high resolution MR imaging techniques.In addition to precise guidance of laser angioplasty and atherectomyprocedures, these apparatus and methods may be used to fully stagelesions and serve as an experimental tool in assessing new therapeuticapplications to atherosclerotic disease. Furthermore, with the resultingintravascular MR imaging system, reliable diagnostic information onatherosclerosis may be obtained and MR-guided interventions may beperformed with high precision.

It will be appreciated, therefore, that the disclosed systems andmethods facilitate enhanced MR imaging and 1-D chemical shift analysisof the interior of a specimen. The loopless antenna 74 provides agenerally uniform sensitivity along the longitudinal axis of the dipoles86, 88 and, as a result of the use of such antenna, facilitates a longerportion of the specimen being imaged with one antenna position. Further,no tuning is required after insertion of the antennas 27, 74, 120 into aspecimen. These antennas, in addition to serving solely as a receiverantenna in one embodiment, may in another embodiment function as atransmitter antenna and a receiver antenna. The disclosed systems andmethods may be employed generally simultaneously with medicalintervention, such as, for example, laser removal of blood vesselplaque.

An embodiment provides enhanced efficiency through the use of at leastone of a balancing transformer and an impedance matching circuit.

EXAMPLE 9

FIG. 16 shows a schematic diagram of an exemplary embodiment of a needleantenna and associated decoupling matching and tuning circuitry. In theillustrated exemplary embodiment, the needle antenna is a biopsy orsample needle 1610 that permits imaging and sampling of a tissuespecimen with a single instrument. A needle according the illustratedexemplary embodiment could be used to obtain a biopsy, or a sample froma variety of structures, including living tissue and inanimate matter.The biopsy needle 1610 and associated circuits 1650 can be fabricatedfrom non-magnetic materials. The biopsy needle 1610 may have a cuttingobturator 1611 with side-cut or side-slit 1612. The needle 1610 may havea hollow core near its distal end 1619. The needle can have a cannula orsheath 1613, which can form the shield portion of an MRI antenna,preferably a loopless antenna, and can be electrically connected to theground or shield side of the decoupling matching and tuning circuit1650, by connection 1651. An extending portion 1640 of the obturator1611, may serve as part of the MRI antenna. The obturator 1611,including a portion 1617 thereof can effectively act as an innerconductor of a coaxial cable portion with an outer conductor formed bythe cannula 1613. A thin-walled electrically insulating layer 1618, maybe located between the obturator 1611 and the cannula 1613. Theinsulator 1618 may extend at least to as far as the ends 1613 a and 1613b of the cannula 1613, to insulate the obturator 1611 in the cannula1613 up to the side-slit 1612. The insulation layer can be any of arange of known electrical insulators including but not limited to apolymer such as a polyester shrink tubing, fluroethylene polymer,tetrafluoroethylene, polyethylene, silicone, metal oxide, glass,polyethylene terephthalate, or the like. The outside of the cannula 1613may be covered with an insulating layer, such as with a biocompatiblepolymer coating.

The biopsy needle 1610 can be connected to decoupling, tuning andmatching circuitry 1650 via, e.g., connections 1651 and 1652. Theseconnections can be made directly via one of the many types of detachableRF connector known to those skilled in the art, or, for convenience, viaan additional section of thin coaxial cable, which can be permanentlyattached to circuitry 1650, or attached via a detachable RF connector.The decoupling, tuning and matching circuitry may include a balun 1653,which serves to balance any currents induced on the biopsy needleantenna at the MRI frequency. This can be formed, for example, from anLC tank circuit made by tuning a coil formed by the outer conductor of acoiled piece of coaxial cable, to the MRI resonance frequency with acapacitor, as is known to those skilled in the RF arts. A capacitor, C₂,may be provided to block direct current from flowing into the antennacircuit. A (PIN) diode D can be connected across the rails that attachto the loop antenna on the proximal side of C₂. A further capacitor, C₃,and an inductor, L₂, can alone or together be added as tuning andimpedance matching elements. The values of L₂ and C₃, in conjunctionwith C₃, are preferably chosen to tune the antenna formed by the biopsyneedle 1610 (cannula 1613 and obturator 1611) to the MRI frequency, andalso to substantially match the impedance to the optimum impedance ofthe MRI scanner receiver input connected at 1661 and 1662. Thisimpedance is preferably that which results in the optimum noise figureof the MRI receiver preamplifier, and is typically 50Ω, thecharacteristic impedance of standard coaxial cable. Connections 1661 and1662 can be formed by 50Ω coaxial cable, or connected directly to theMRI receiver input.

Diode D can decouple the antenna during the period when the RF pulsesare applied to excite MRI signals. During MRI excitation by an externaltransmit coil, a DC bias voltage may be provided by the MRI scanneracross the coil input, causing the diode to conduct. During conduction,the tuning elements can be shorted-out, which results in detuning of theloopless antenna biopsy needle, and high impedance, thereby limitingthose RF currents induced at the MRI frequency in the loop.

FIG. 17 illustrates exemplary electrical connections of the exemplarybiopsy needle MRI antenna described above in connection with FIG. 16,and a plunger mechanism for activating the acquisition of a biopsyspecimen, in accordance with an embodiment. The cannula 1713, which canfunction as the shield, may be electrically connected to a loadingspring 1720 by a joint 1721. The spring 1720 may be non-magnetic. Joint1721 may be a wire. The spring 1720 can thereby serve two purposes.First, the spring 1720 may act as a compression spring to load andtrigger the movement of the cannula 1713 that cuts the tissue. Second,the spring 1720 can act as a deformable conductor that connects theshield that can be formed at least in part by the cannula 1713, to thematching circuitry 1650 at connector 1651 in FIG. 16. The electricalconnection can be made, e.g., by connecting the spring 1720 to lead1651, which in an embodiment is the outer shield of a section offlexible coaxial cable.

The proximal end 1711 a of the obturator 1711 can be secured to, e.g., aplunger button 1722. The proximal end 1711 a may be covered with, e.g.,ultraviolet cure adhesive. An electrical connection 1723 can be madefrom the proximal end 1711 a of the obturator 1711, which can form theinner conductor of an MRI antenna, to the connection 1652 of the tuningmatching and decoupling circuit 1650, as depicted in FIG. 16. In anembodiment, the device may include a flexible coaxial cable connection(not shown) between the needle antenna and circuitry 1650. Connection1652 may preferably be the inner conductor of the coaxial cable.

FIGS. 18 and 19 depict two exemplary positions that a biopsy needle canadopt. FIG. 18 shows a biopsy needle 1810 in a charged position. In thisposition, the spring 1820 is compressed. The obturator 1811 can berigidly coupled to the plunger 1822 and slideably displaceable relativeto the cannula 1813. As the plunger 1822 is pulled in a proximaldirection, a plastic clip 1890 can compress the spring 1820. Theside-slit 1812 of the obturator 1811 can be exposed, and the cannula1813 can be retracted relative to the obturator 1811. FIG. 19 depicts abiopsy needle 1910 in an uncharged position. The spring 1920 can berelaxed. The side-slit 1912 of the obturator 1911 can be covered by thecannula 1913. A biopsy 1980 can be coupled to the biopsy needle antenna1910. In this exemplary embodiment, the biopsy 1980 is trapped betweenthe cannula 1913 and the obturator 1911, in the side-slit 1912.

With reference to FIG. 18, to operate the tissue sampling function ofthe biopsy needle 1810, the plunger 1822 can be pulled in the proximaldirection, which can charge the loading spring 1820 until a lockingmechanism (not shown) locks in place. The locking mechanism may include,e.g., a notch. Once the spring is locked, the plunger 1822 may be freelypushed or pulled, thereby advancing or retracting the obturator 1811 outfrom or into the cannula 1813, respectively. A high quality image may beobtained in a variety of obturator positions, particularly when theobturator 1811 is extended from the cannula 1813, as depicted. Once theneedle has been positioned for the biopsy or sampling, the plunger 1822may be forcefully pushed distally. This can release the lockingmechanism so that the cannula 1813 is propelled forward by the releasingspring 1820. A sharp-edged front-end 1813 b of the cannula cuts thetissue sample intact within the slide-slit portion 1812 as the biopsyneedle transitions to the state depicted in FIG. 19.

FIG. 20 illustrates an exemplary embodiment of an obturator 2011 in moredetail. The obturator 2011 can have a distal end 2070. The distal end2070 can be sharp and designed for piercing, e.g., tissue. The obturator2011 can have a side-slit 2012 for receiving a portion of a tissue as abiopsy (not shown). The obturator 2011 can have a shaft 2017. The shaftcan serve as the inner conductor of a coaxial cable. The obturator 2011can be covered by an insulator 2018. The insulation may include, forexample, a shrink-tubing that can fit snugly over the obturator 2011.The insulator can fill the space between the obturator 2011 and acannula (not shown). The insulator 2018 can fill a portion of the spacebetween the obturator 2011 and the cannula. Air can fill at least aportion of the space between the obturator 2011 and the cannula. Theinsulator may include a lubricious substance to facilitate sliding ofthe cannula over the obturator 2011, or sliding of the obturator 2011within the cannula. A lubricious coating (not shown) may cover theinsulator 2018 for similar purposes. The insulator 2018 and lubricioussubstance or coating may include suitable materials described herein. Inan embodiment, the obturator 2011 has a diameter of 0.067″ at distalregion 2017 b and proximal region 2017 a, and a reduced diameter of0.055″ in region 2017 c to accommodate an insulation layer of 0.010″thickness. In an embodiment, the movement of the obturator 2011 insidethe cannula 2013 is not obstructed. The thin section can be covered withelectrical insulation 2018, as detailed above. Insulation 2018 canfunction as both electrical insulation and dielectric portion of theantenna. The specific dimensions described are provided for illustrativepurposes and are not intended to be limiting. It will be understood toone skilled in the art that such needle biopsy antenna devices can befabricated for a variety or range of different sizes, for example, withan obturator diameter in the range of 0.03″ to 0.15″.

FIG. 21 shows a block diagram illustrating the operation of an MRIscanner system, which may be used in connection with an embodiment. Amagnet can provided for creating the magnetic field necessary forinducing magnetic resonance. Within the magnet can be X, Y, and Zgradient coils for producing a gradient in the static magnetic field inthree orthogonal directions. Within the gradient coils may be anexternal RF excitation coil. The external RF excitation coil can producethe magnetic field necessary to excite the MRI signals in the body. Acomputer can be provided for controlling all components in the MRIscanner. This includes the RF frequency source, spectrometer and pulseprogrammer. The pulse programmer can generate a controlled time-sequenceof shaped and/or phase or frequency-modulated RF pulses that aredelivered to the RF power amplifier. The RF power amplifier may havepulse power of 1–20 kW, which is applied to the external RF excitationcoil. The computer can also control the gradient magnetic field byproviding a sequence of modulated pulses that are synchronous with theRF pulse sequence, to gradient power amplifiers, which in turn activatethe X, Y, and Z gradient magnetic field coils in the magnet. Signalsdetected by receiver coils in response to the applied RF/gradientimaging sequences, including those detected in the aforementionedmulti-functional MRI catheter system, can be coupled to a receiverpreamplifier. These signals may be amplified, phase sensitive detected,for example, by converting to digital signals and being fed to a digitalreceiver. The digital image data may then be reconstructed in thecomputer and displayed as images on a monitor or the like.

An embodiment provides accurate localization of the biopsy needle tip.Because the needle antenna is a receiver it can be used to directlyimage the tissue around it. This image can be viewed on with highresolution employing the needle antenna receiver disclosed herein, or,it can be viewed at low resolution as an overlay on a largefield-of-view “scout” image obtained with an auxiliary coil outside thebody. The location of the needle antenna can be tracked in the body, bythe bright line of signal moving in the scout image. The scout image canbe updated at an interval set by the user to compensate for patientmotion. An interactive control can allow the physician to “zoom in”towards the bright catheter, finally resulting in a high-resolutionimage in the area of the distal needle tip. The “zoom” function can beachieved with interactive control of the imaging gradients.

EXAMPLE 10

FIGS. 22A and 22B show images acquired with an MRI biopsy needle. FIG.22A depicts a bovine kidney with a biopsy needle antenna insertedtherein. The uniform signal intensity of the kidney is typical of renalMRI imaging. The needle antenna is clearly discernable. FIG. 22B depictsa lemon with a biopsy needle antenna inserted therein. The radiatingfibrous structure is readily visible, as are seeds inside the lemon. Thebiopsy needle position is accurately localized with respect to thelemon.

FIGS. 23A–F depict a sequence of images from an image-guided biopsyprocedure. FIG. 23A depicts the initial introduction of a biopsy needleantenna into the pig anatomy. FIG. 23B depicts deeper insertion. FIG.23C depicts full insertion of the biopsy needle antenna prior to biopsyacquisition. FIG. 23D depicts the biopsy needle antenna after biopsyacquisition. FIG. 23E depicts withdrawal of the biopsy needle antenna.FIG. 23F depicts the pig anatomy after the biopsy needle has beenwithdrawn completely.

Preferred embodiments may include an MRI biopsy needle; an MRI biopsyneedle connected and used in conjunction with matching tuning decouplingcircuitry; an MRI biopsy needle and matching tuning decoupling circuitryused in conjunction with an MRI scanner; and a method for performingimage-guided biopsies employing an MRI biopsy needle antenna, tuningmatching and decoupling circuitry in conjunction with an MRI scanner.

While for clarity of disclosure reference has been made herein todisplay means for displaying an image, it will be appreciated that theimage information may be stored, printed on hard copy, be computermodified, or be combined with other data. All such processing shall bedeemed to fall within the terms “display” or “displaying” as employedherein.

Various alternative embodiments are envisioned within the scope of thedisclosed systems and methods. Figures provide illustration of someinventive aspects of the disclosed systems and methods. Therefore,relative or absolute dimensions in the Figures should be understood asexemplary and not as limiting. Whereas particular embodiments have beendescribed herein for purposes of illustration, it will be appreciated bythose skilled in the art that numerous variations of the details may bemade without departing from the disclosed systems and methods asdescribed in the following claims.

1. A biopsy needle antenna, comprising: a magnetic resonance imagingantenna, having: an outer shield; and an inner conductor electricallyinsulated from the outer shield by a dielectric; and a biopsy needleelectrically connected to the inner conductor and electrically insulatedfrom the outer shield by the dielectric.
 2. The biopsy needle antenna ofclaim 1, further comprising a sheath, the biopsy needle being slideablydisplaceable within the sheath.
 3. The biopsy needle antenna of claim 2,wherein the sheath is defined by the outer shield.
 4. The biopsy needleantenna of claim 1, wherein at least one of the outer shield, the innerconductor, and the biopsy needle comprise a magnetic resonancecompatible material.
 5. The biopsy needle antenna of claim 1, whereinthe biopsy needle antenna is configured with circuitry that receivesmagnetic resonance spectroscopy information from a sample.
 6. The biopsyneedle antenna of claim 1, wherein the outer shield and the innerconductor form a coaxial cable.
 7. The biopsy needle antenna of claim 6,wherein the coaxial cable is electrically interconnected to an impedancematching circuit.
 8. The biopsy needle antenna of claim 1, wherein atleast one of the outer shield, the inner conductor, and the biopsyneedle comprise a superelastic material.
 9. The biopsy needle antenna ofclaim 1, wherein the outer shield is slideably displaceable with respectto the inner conductor.
 10. The biopsy needle antenna of claim 1,wherein the inner conductor comprises an obturator and the outer shieldcomprises a cannula slideably displaceable over the obturator.
 11. Thebiopsy needle antenna of claim 10, wherein the obturator furthercomprises a side-slit.
 12. The biopsy needle antenna of claim 11,wherein the cannula comprises a distal end having a cutting edge, thecutting edge slideably displaceable over the side-slit.
 13. The biopsyneedle antenna of claim 11, wherein the cannula covers at least theside-slit.
 14. The biopsy needle antenna of claim 10, wherein thecannula is spring-loaded.
 15. The biopsy needle antenna of claim 10,wherein at least a portion of the obturator protrudes from a distal endof the cannula.
 16. The biopsy needle antenna of claim 1, furthercomprising a spring coupled to the outer shield.
 17. The biopsy needleof claim 16, wherein the spring is electrically coupled to the outershield.
 18. The biopsy needle antenna of claim 1, wherein the dielectriccomprises at least one of fluroethylene polymer, tetrafluoroethylene,polyester, polyethylene, silicone, metal oxide, glass, and polyethyleneterephthalate.
 19. The biopsy needle antenna of claim 1, wherein thedielectric is covered by a lubricious coating.
 20. The biopsy needleantenna of claim 19, wherein the lubricious coating comprises at leastone of polyvinylpyrrolidone, polyacrylic acid, and silicone.
 21. Thebiopsy needle antenna of claim 1, wherein the inner conductor and outershield are electrically coupled to an interface.
 22. The biopsy needleantenna of claim 21, wherein the interface comprises at least one of atuning-matching circuit, a balun circuit, a decoupling circuit, and avariable capacitor.
 23. The biopsy needle antenna of claim 21, whereinthe interface resides upstream of the biopsy needle and is configured tocouple to an MRI scanner.
 24. A sampling needle antenna, comprising: acannula being formed at least in part of a conductive material anddefining an outer shield; an obturator being formed at least in part ofa conductive material and defining an inner conductor, the obturatorbeing slideably displaceable relative to the cannula; and an insulatorelectrically insulating the cannula from the obturator; wherein theouter shield, the inner conductor, and the insulator form a magneticresonance imaging antenna.
 25. A method of obtaining a sample withmagnetic resonance imaging guidance, comprising: providing a magneticresonance imaging antenna, wherein the magnetic resonance imagingantenna comprises an outer shield and an inner conductor electricallyinsulated from the outer shield by a dielectric, and wherein a samplingneedle is electrically connected to the inner conductor and electricallyinsulated from the outer shield by the dielectric; advancing the antennato a structure from which the sample is to be taken; detecting magneticresonance data by the antenna; and coupling the sample to the antennaand the sampling needle whereby the sample is obtained.
 26. The methodof claim 25, wherein the sample is a biopsy.
 27. The method of claim 25,wherein the inner conductor comprises anobturator and the outer shieldcomprises a cannula, the obturator slideably displaceable relative tothe cannula.
 28. The method of claim 25, further comprising coupling themagnetic resonance data to an MRI scanner to form a magnetic resonanceimage.
 29. The method of claim 28, wherein the image formed is acomposite image.
 30. The method of claim 28, wherein the image formed isa high resolution image.
 31. A method of obtaining a sample withmagnetic resonance imaging guidance, comprising: providing a samplingneedle magnetic resonance imaging antenna; advancing the antenna to astructure from which the sample is to be taken; detecting magneticresonance data by the antenna; and coupling the sample to the antenna,wherein the antenna comprises a cannula including an outer shield, anobturator including an inner conductor, the obturator slideablydisplaceable relative to the cannula, and an insulator electricallyinsulating the outer shield from the inner conductor; and wherein thecoupling includes trapping the sample between the cannula and theobturator.
 32. The method of claim 31, wherein trapping includes movingat least one of the cannula and the obturator relative to the other. 33.A method of obtaining a magnetic resonance imaging-guided biopsy,comprising: providing a biopsy needle antenna, having: a magneticresonance imaging antenna, including: an outer shield; and an innerconductor electrically insulated from the outer shield by a dielectric;and a biopsy needle electrically connected to the inner conductor andelectrically insulated from the outer shield by the dielectric;advancing the needle to a lesion; imaging the lesion with the antenna;and taking a sample of the lesion with the needle.